Improve sections

assets/anchors.js

@@ -0,0 +1,11 @@
+(function () {
+    document.querySelectorAll('.content h1, .content h2, .content h3, .content h4, .content h5, .content h6').forEach(function (h) {
+        if (!h.id) return;
+        var a = document.createElement('a');
+        a.href = '#' + h.id;
+        a.className = 'heading-anchor';
+        a.setAttribute('aria-label', 'Link to this section');
+        a.textContent = '§';
+        h.insertBefore(a, h.firstChild);
+    });
+}());

assets/page.html

@@ -81,6 +81,7 @@
             {{end}}
             {{if or .Content .SpecialContent}}
             <script src="/_/content.js"></script>
+            <script src="/_/anchors.js"></script>
             <script src="/_/toc.js"></script>
             {{end}}
             {{if .Content}}

assets/style.css

@@ -234,6 +234,15 @@ main {
     max-width: 100%;
 }
 
+.heading-anchor {
+    color: var(--text-muted);
+    margin-right: 0.4em;
+    font-weight: normal;
+}
+.heading-anchor:hover {
+    color: var(--primary-hover);
+}
+
 /* === File listing === */
 .listing {
     border: 1px solid var(--secondary);

assets/toc.js

@@ -21,7 +21,7 @@
     var a = document.createElement("a");
     a.href = "#" + h.id;
     var clone = h.cloneNode(true);
-    clone.querySelectorAll(".btn, .muted").forEach(function (el) { el.remove(); });
+    clone.querySelectorAll(".btn, .muted, .heading-anchor").forEach(function (el) { el.remove(); });
     a.textContent = clone.textContent.trim();
     li.appendChild(a);
     list.appendChild(li);

main.go

@@ -243,6 +243,7 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 	}
 	content := r.FormValue("content")
 	indexPath := filepath.Join(fsPath, "index.md")
+	redirectTarget := urlPath
 
 	// If a section index was submitted, splice the edited section back into
 	// the full file rather than replacing the whole document.
@@ -258,6 +259,15 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 			sections[sectionIndex] = []byte(content)
 		}
 		content = string(joinSections(sections))
+		// Section index ≥ 1 is a heading-anchored section. Redirect to its
+		// anchor so the user lands on the section they just saved, even if
+		// the heading text changed.
+		if sectionIndex >= 1 {
+			ids := headingIDs([]byte(content))
+			if sectionIndex-1 < len(ids) {
+				redirectTarget = urlPath + "#" + ids[sectionIndex-1]
+			}
+		}
 	}
 
 	if strings.TrimSpace(content) == "" {
@@ -275,7 +285,7 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 			return
 		}
 	}
-	http.Redirect(w, r, urlPath, http.StatusSeeOther)
+	http.Redirect(w, r, redirectTarget, http.StatusSeeOther)
 }
 
 // readPageSettings parses a .page-settings file in dir.

sections.go

@@ -3,6 +3,9 @@ package main
 import (
 	"bytes"
 	"regexp"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/text"
 )
 
 var sectionHeadingRe = regexp.MustCompile(`(?m)^#{1,6} `)
@@ -25,6 +28,29 @@ func splitSections(raw []byte) [][]byte {
 	return sections
 }
 
+// headingIDs returns the auto-generated id of every heading in raw markdown,
+// in document order. The kth heading (1-indexed) corresponds to section k from
+// splitSections. Uses the package-level goldmark parser so duplicate-id
+// numbering matches what the renderer emits.
+func headingIDs(raw []byte) []string {
+	doc := md.Parser().Parse(text.NewReader(raw))
+	var ids []string
+	ast.Walk(doc, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+		if _, ok := n.(*ast.Heading); ok {
+			if v, ok := n.AttributeString("id"); ok {
+				if b, ok := v.([]byte); ok {
+					ids = append(ids, string(b))
+				}
+			}
+		}
+		return ast.WalkContinue, nil
+	})
+	return ids
+}
+
 // joinSections reassembles sections produced by splitSections.
 // Inserts a newline between sections when a non-empty section lacks a
 // trailing newline, so an edited section cannot inline the next heading.